1. Field of the Invention
The present invention relates to an apparatus and method for controlling the quantity of fuel over a common rail diesel engine, and more particularly, to an apparatus and method for controlling the quantity of fuel over a common rail diesel engine, which make it possible to reduce a deviation in the quantity of injected fuel using a map having a fuel temperature and a rail pressure as variables of a pressure wave correction (PWC) logic, reduce exhaust gases from the common rail diesel engine, and improve fuel efficiency of the common rail diesel engine.
2. Description of the Related Art
In general, the fuel injection system of a common rail diesel engine includes an injection pressure generating process and an injecting process, both of which are completely separated from each other. Thus, the common rail system can freely design burning and injecting processes because the injection pressure generation of fuel can be regarded separately from injection of fuel in the design of the engine. In detail, since both injection pressure and injection timing of the fuel can be regulated according to conditions of engine operation using an engine map, the fuel can be injected at high pressure even when revolutions per minute (rpm) of the engine is low, so that complete combustion can be accomplished. Further, pilot injection allows exhaust gases and noise to be further reduced, and the fuel injection is hydraulically controlled by a nozzle needle, so that it can be rapidly controlled until the injection is completed.
With the development of diesel engine technologies, there has recently been developed technology that performs multiple injections on diesel fuel during each combustion stroke.
FIG. 1 is a graph showing a change in the pressure of fuel during injection of fuel.
As can be seen from the graph of FIG. 1, in the case of multiple injections of fuel, a quantity of fuel injected later is affected by a quantity of fuel injected previously as well as a time difference between two injections of fuel, because the pressure is varied in a rail, a high-pressure pipe, and injectors.
This variation of the pressure causes a difference between quantities of injected fuel. In order to correct the difference between quantities of injected fuel, correction logic is used.
FIG. 2 conceptually illustrates the correction logic of a conventional apparatus for controlling the quantity of fuel over a common rail diesel engine.
As illustrated in FIG. 2, the correction logic properly corrects the quantity of fuel using a base map and an amplitude map. The base map is adapted to obtain a normalized reference valve on the basis of a time difference between two fuel injections and a fuel quality required for the second injection. The amplitude map is adapted to obtain a correction weight of the quantity of fuel by both a fuel quality required for the first injection and pressure in the rail.
FIG. 3 is a graph showing a change in the quantity of fuel caused by rail pressure of a conventional common rail diesel engine.
In FIG. 3, the change in the quantity of fuel is measured with respect to five rail pressures of 250 bar, 300 bar, 800 bar, 1200 bar and 1400 bar. This data is used when the base map of an existing logic is prepared. However, depending on a change in pressure, a waveform showing the change in the quantity of fuel is shifted, and a period (or frequency) of the waveform is varied. As such, the preparation of a map representative of all the cases using a single curve not only provides very low accuracy, but also requires much time and high expenses to a future verification test and re-correction.
Further, all of the existing correction logics are adapted to prepare the base and amplitude maps on the basis of the same time, so that the maps prepared so as to be well matched on some time sections are not well matched on other time sections.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.